Methods for measuring the direction of incidence of a wave are known. For example, document DE 44 21 191 A1 describes one such method.
As shown in FIG. 1, the receiver generally includes an array of antennas 10, including N antennas, preferably identical to one another. In FIG. 1, N is equal to six.
The antennas are distributed along a plane XY transverse to the axis Z of a support mast, positioned substantially vertically.
In this horizontal plane XY, the antennas are positioned so as to have the pointing directions equally distributed in terms of angle within the angular domain to be covered. For example, they may be positioned over a regular polygon, a hexagon in FIG. 1.
Each antenna has a radiation pattern having a maximum along its pointing axis Ai.
The radiation pattern of an antenna has a large opening at 3 dB, typically about 50° to 120°.
The main lobes of the radiation patterns of the antennas overlap one another such that the array covers 360° in the horizontal plane XY.
Each antenna is capable of covering a very wide frequency band, typically of about ten GHz, situated within a frequency range extending between 10 MHz and 100 GHz, preferably between 100 MHz and 50 GHz.
For an instantaneous wideband receiver, the measurement of the direction of incidence D of the incident wave, i.e., the determination of a bearing angle Θ0 in the plane XY, is obtained by carrying out an amplitude goniometry method. This method takes advantage of the fact that the characteristics of the antennas are identical, but that only their orientation relative to the incidence direction D of the wave changes. The measurement of the incidence direction D is then obtained for example by interpolation of a normalized radiation pattern characteristic of the type of antenna by the amplitudes of the signals generated by each antenna.
However, the known methods for measuring the direction of incidence of a wave have several drawbacks.
First, the obtained measurement is relatively imprecise. It is typically obtained with a precision of between 3 and 10°.
Lastly, the measurement is limited to only the horizontal plane XY, i.e., the determination of the bearing angle. It is consequently biased by the position of the source of the electromagnetic wave outside the plane XY, i.e., biased by the elevation angle Φ0 of the direction of incidence.
It should be noted that instantaneous wideband antennas are known, for example from document U.S. Pat. No. 3,229,293 A, including at least four radiating elements each forming a strand, the strands being wound in spirals around a same center in a plane transverse to the pointing axis of the antenna. The antenna then includes four supply points, for which a beam formation of the two-plane monophase type is possible, by phase shifting the different supply points relative to one another, for example by 90°. In this case, a measurement of the incidence direction along two planes, i.e., bearing and elevation, can be obtained. However, this type of antenna uses a complex technology, in particular in very wideband cases, and requires four excitation or reception channels (depending on whether the antenna is used as a transmitter or a receiver).